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L'interazione terreno-rivestimento in gallerie sostenute con calcestruzzo proiettato
Full text linkNella presente nota vengono descritti i risultati dell’attività’ di ricerca riguardante la modellazione e l’analisi di gallerie sostenute da un pre-rivestimento di calcestruzzo proiettato. Una prima fase del lavoro ha avuto come oggetto la messa a punto di tecniche semplificate in grado di fornire una stima di prima approssimazione del livello di sollecitazione raggiunto nel rivestimento in funzione delle caratteristiche del terreno e della modalità’ costruttive della galleria. Per una valutazione più’ precisa delle condizioni statiche nel terreno e nel rivestimento si e’ resa necessaria successivamente l’adozione di un modello costitutivo per il calcestruzzo proiettato in grado di descrivere i complessi fenomeni legati alla maturazione del materiale nel tempo
IL CALCESTRUZZO PROIETTATO COME ELEMENTO STRUTTURALE NELL'ESECUZIONE DEGLI SCAVI IN SOTTERRANEO
No full textShort and long-term load conditions for tunnels in low permeability ground in the framework of the convergence-confinement method
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Influence of rock mass parameters on the performance of a TBM in a gneissic formation (Varzo tunnel)
No full textThe paper analyses the influence of rock mass quality on the performance of a double shield TBM in the excavation of a tunnel in a gneiss formation wich is characterized by high strength and low fracture intensity. The geomechanical survey of the tunnel face was performed during maintenance downtime and the observed conditions were correlated with the machine performance parameters for that same day. A statistical analysis of the data shows that penetration rate correlates well with a slightly modified RMR index (in wich the influence of the water conditions and joint orientation were discounted), but the most important factor is by far the partial rating of the RMR classification related to joint spacing only. However in tunnels characterized by greater variability in rock strength and joint conditions, it could be worthwhile using the complete RMR index. Given the toughness of the rock, failure of the cutter bearing and supports were a frequent occurrance during excavation. Owing to this factor the influence of rock quality on the rate of advance was found to be weak and the correlation more scattered. The results obtained for the Varzo tunnel were compared with those relative to other tunnels in granitic rocks and found to be in good agreement. However the relationships obtained should be considered valid only for this type of rock; machine behaviour could be found to be markedly different in other rock types, even where rock material strength and joint frequency are the same
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